October 14 – Battle on the Elster between the armies of the two rival brothers-in-law kings of the German states, Henry IV, King of the Romans and Rudolf of Rheinfelden meeting at the White Elster river in the Great Saxon Revolt civil war of the Holy Roman Empire. Rudolf is the victor but dies the following day at Merseburg of wounds received.
King William I of England, in a letter, refuses to accept Pope Gregory VII as his overlord.
c. 1080–1100 – The Master of Daphni creates the mosaic of Christ Pantocrator in the central dome of the katholikon at Daphni Monastery in Greece.
The Rubenid Principality of Cilicia gains independence after its founder, Ruben I, Prince of Armenia, succeeds in establishing his authority in the mountainous regions of Cilicia (approximate date).
The Seljuq-led Turkish tribes begin the Great Turkish Invasion of the Kingdom of Georgia.
The Song dynasty Chinese polymath scientist and statesman Shen Kuo begins his defensive military campaign against the Tangut people of the Western Xia Kingdom, successfully defending the invasion route to Yan'an.